The present invention relates to a separation device comprising a vessel having an essentially circular cylindrical shape around a center axis, a first passage provided in the cylindrical wall of the vessel, a second passage, provided in the cylindrical wall of the vessel on a diametrically opposite part thereof, and an enclosure means provided in the vessel to enclose a bed of particulate material and comprising a first and second enclosure panel provided inside the first and second passage, respectively, at a distance therefrom to provide a flow distribution space therebetween and being perforated to permit fluid flow therethrough.
It is known to produce gases, such as oxygen and nitrogen, by the separation of air, Furthermore, it is known to provide such a separation by means of a so called PSA-process (Pressure Swing Adsorption). A conventional PSA-process uses one or more adsorption beds containing an adsorbent provided in one or more layers. Typically, the adsorbent comprises molecular sieves particles having a size of 1-2 mm. During the PSA-process the gas is flowing through the adsorption bed, whereby the flow rate and the direction of the gas is changing during the different phases of the process. In order to increase the process efficiency, it is necessary with a bed which allows high gas flow rates in all directions of flow. However, in a conventionally constructed adsorption bed the flow rate of the gas is limited in one of the two directions by the risk of fluidization of the bed material. Fluidization leads to immediate destruction of the bed material. Thus, the risk for fluidization is a limiting factor when developing new more efficient processes.
In a conventional adsorption bed, it is relied on the gravitation to avoid fluidization of the bed material and thus the gas flow is vertically directed. Due to the gravitation the flow rate in a downward direction may be higher than in an upward direction. Normally, during the adsorption phase the gas flow is directed upwardly and during the regeneration phase the gas flow is directed downwardly.
A vessel for a conventional adsorption bed normally has the shape of a circular cylinder, thereby providing sufficient structural strength to the vessel. The vessel is provided with its center axis vertically directed and the gas is flowing through the vessel along the center axis. The absorption bed is constructed such that it has an essentially constant cross-section area in order to provide optimal conditions during the adsorption phase, i.e. the gas flow will be distributed equally in all parts of the adsorption bed and thus the adsorption conditions will be equal. This is easily achieved by means of an upper and lower plane panel limiting the adsorption bed and being perforated to permit gas flow therethorugh. However, the possible length of the bed seen in the flow direction is limited due to the pressure drop in the bed. For larger separation systems, the bed therefore has to be arranged in an horizontal cylinder vessel. Thereby, the adsorption bed is defined by an upper and lower plane panel, being perforated and extending in parallel with the horizontally directed center axis, and parts of the cylindrical wall of the vessel between these panels. The upper panel is floating on top of the bed material and gives only a small contribution to prevent fluidization. The gas will flow through an inlet in the cylindrical wall of the vessel to a flow distribution space between the cylindrical wall and one of said panels, through the bed and to another flow distribution space between the cylindrical wall and the other of said panels, and through an outlet in the cylindrical wall of the vessel. However, the gas flow through the bed of such a horizontal cylindribal vessel will not be distributed equally, because of the cylindrical walls of the vessel. This means that the gas flowing in the middle will pass the adsorption bed faster than the gas flowing closer to the cylindrical walls and consequently the adsorption front of the flow will not be plane. Such flow conditions are not optimal in respect of the process efficiency.
EP-A-480 797 discloses an adsorber for the separation of a gaseous mixture. The adsorber comprises an enclosure containing a mass of adsorbing particulate material. The enclosure has an elongated shape and comprises two longitudinal perforated plane shaped panels being separated from and parallel to each other. The panels and parts of the enclosure wall defines a chamber containing the particulate material. The enclosure is provided in a vertical orientation and thus the gas flow therethrough is horizontal. On top of the particulate material, there is provided a flexible wall outside which is formed a closed space to be pressurized in order to maintain the particulate material in a fixed position within the bed. The particulate material is provided in two successive layers, seen in the direction of the gas flow, with different particle sizes in the two layers.